1. Field of the Invention
The present invention relates to an air conditioning apparatus for an automobile, wherein a refrigeration cycle of a refrigerant is carried out, and more particularly, to a coupling for connecting pipes made of an aluminum material to thereby create passages for carrying the refrigerant.
Throughout the specification the term aluminum includes not only pure aluminum but also any alloy based on aluminum, except where otherwise defined.
2. Description of the Related Art
Current requirements for a reduction of the weight of an automobile, as much as possible, have led to a requirement for a similar reduction of the weight of an air conditioning apparatus used in the automobile. To reduce the weight of an air conditioning apparatus, pipe couplings used in the air conditioning apparatus must have as low a weight as possible, and to obtain such a light weight pipe coupling, a coupling has been proposed that is constructed by a pair of flanges made of aluminum and mounted at each ends of pipes to be connected. These flange members mounted at the ends of the pipes are connected to each other to thereby connect the pipes. (See Japanese Unexamined Patent Publication No. 60-43416).
Nevertheless, in view of the high pressure of the refrigerant flowing through the pipes, the strength of the pipe couplings constructed by the flanges made of aluminum is too low unless the flange is provided with a large outer diameter, but a flange having such a large outer flange is not desirable from the viewpoint of an efficient utilization of space.
Therefore, it has been proposed to use an inner flange made of a steel material and arranged between a pipe and an outer flange both made of aluminum. Such a construction, however, allows a contact between different materials, i.e., aluminum and steel, and this generates an electromotive force between the flange made of steel and the pipe made of aluminum, and accordingly, a more rapid corrosion of the metal parts. Depending on the components of the steel used for the flange, a corrosion of the pipes may occur, and thus the refrigerant under a high pressure may be leaked to the outside.